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LED - RGB changeable strips - anyone use them?


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#1 Albion Hockney

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Posted 03 March 2015 - 02:01 PM

I have a MV project and was thinking about using some LED light strips to wash backgrounds and sometimes be in frame. Looking for a strong monochromatic coloring.

 

These LED light strips seems like a great solution, I was just curious if anyone has used them and to try to get a sense of how much light they put out.

 

Im shooting 800asa as a 2.8 mostly so I dont need a ton of light. One thing we were thinking about is hiding them under the awning of a motel and washing the whole front in a color. Will one strip running the length of the motel be enough light do you think? does anyone know where you can see photometrics....I'm sure they all vary a bit but Im basically looking at the IKEA/home improvment store variety of these lights.

 

 

 


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#2 aapo lettinen

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Posted 03 March 2015 - 02:59 PM

the white led stripes I have used draw about 2.9 amperes max per 5m length, this is 60led/m with the bigger leds. it's about 35 watts per 5m which is not that much, you can do a little better with 120led/m stripes but their output and color varies even more than the 60/m versions.

These were for cool white stripes but I believe you could get somewhat similar results with rgb stripes. You could install two stripes side by side to get more output .

 

It is noteworthy that the Chinese led stripes have HUGE variations in output, durability, color reprod, color temperature, overall quality and it is best to first test the possible candidates and then order the rest of the leds making sure they are the exactly same model and batch than the tested one. The Chinese ebay sellers seem to sell batch at time basis and if you're not quick enough you may miss the good ones and it may take some time to get even remotely matching alternative. as said, the Chinese stuff has huge variations and they don't usually match at all unless they are all from exactly the same production batch  :blink:  

This should not be a problem if you purchase the stripes locally. then you could also test them out (bring a multimeter/amp meter with you and you can test how much they approximately draw power)  :)


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#3 James Compton

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Posted 03 March 2015 - 04:57 PM

I have a MV project and was thinking about using some LED light strips to wash backgrounds and sometimes be in frame. Looking for a strong monochromatic coloring.

 

These LED light strips seems like a great solution, I was just curious if anyone has used them and to try to get a sense of how much light they put out.

 

Im shooting 800asa as a 2.8 mostly so I dont need a ton of light. One thing we were thinking about is hiding them under the awning of a motel and washing the whole front in a color. Will one strip running the length of the motel be enough light do you think? does anyone know where you can see photometrics....I'm sure they all vary a bit but Im basically looking at the IKEA/home improvment store variety of these lights.

 

 

 

 Test. Conduct plenty of tests. That will prevent any surprises. I've talked to a few rigging gaffers on some very big budget movies here in Atlanta that were caught off guard when the set decorators installed cheap LED tape lights in that background that caused flicker on-camera. When you shooting any LED tape that isn't 'LITE GEAR' brand, you HAVE TO TEST. There is a brand called 'HIT LIGHTS', that makes a 300 diode 16ft roll of RGB, Warm White and Cool White that has passed the test with some of the studio level shoots in town.


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#4 Phil Rhodes

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Posted 03 March 2015 - 06:50 PM

This is probably clear to most people, but it's worth being explicit that flicker problems will be caused by the drivers, not the LEDs themselves. The sort of drivers used on colour mixing LEDs (whether tape or some other form factor) invariably use PWM. Some may be fast enough to avoid objectionable flicker at some frame rates, but rolling shutter cameras can be a real difficulty in this regard. If you need real time RGB colour mixing, you can get small DC-DC converters very cheaply from chinese suppliers (look on ebay) which will, in my experience, provide very good, direct-current control of LEDs which should avoid flicker. I built some into little aluminium cases with convenient controls and voltmeters for this purpose. If you need real-time, on-shot control, as from a DMX lighting desk, you may be in a bit of a bind. I'm not aware of a good solution.

 

Yes the white stuff is completely inconsistent. The coloured stuff is much better - the light output is very much set by the underlying physics of the device - but they can still have brightness offsets. The fact that they are so monochromatic can be a problem, with the individual colours often looking very much different on camera than they do to the eye. This is particularly the case with the blue, which can end up looking almost purple. If in doubt, get white, and lay a strip of gel over the top of it. Horribly inefficient and not nearly as bright, but it should behave better.

 

P


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#5 Guy Holt

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Posted 17 March 2015 - 08:55 PM

I have a MV project and was thinking about using some LED light strips to wash backgrounds and sometimes be in frame. ... we were thinking about hiding them under the awning of a motel and washing the whole front in a color. Will one strip running the length of the motel be enough light do you think? 

 

As I am discovering, a lot of LED AC power supplies are not power factor corrected. Which means that if you do not take their poor power factor (which can be as low as .45) into account when running LED Ribbons the length of the motel you can find yourself tripping breakers because the lights will draw twice the current you would think.  A good example of this was a Christmas movie shot here this last January.  The set decorators dressed a large tree (20’ high) with hundreds of LED strings. Where each string was just a few watts they figured they could plug them all into one circuit. After the breaker tripped several times, only then did they call in the electricians to sort out the mess. But of course now the production is waiting for the tree lights to come on before they can shoot and the electricians caught the blame.

 

LED_481PQ_Wkshp_LiteRibbon_PF.jpg

(The LiteGear RGB Lite Ribbon pictured above has a pf of .45)

 

Unfortunately, the manufacturers of LED Light fixtures generally do not give power factor specifications for their products. One would think that the less expensive LED lights would not be pfc, while the more expensive ones would, but that proved not to be the case in recent testing of fixtures. Over half of the fixtures that I tested at random (from the inventories of Boston area rental and lighting sales companies) were not pfc. With power factors ranging from .45 to .63, these fixtures generated considerable harmonic distortion (THD ranged from 75-85%.) Even those that were pfc generated harmonic currents when dimmed. For instance, the pfc of the new Litepanel Astra 1x1 dropped from .99 to .54 when dimmed 50% (THD increased to 83.2%.) 

 

One could argue that the wattage of LED fixtures is so low that the harmonics they draw and kick back into the electrical distribution system is so low that it does not matter from a practical standpoint. While that is true to a degree, when used as the predominant source of light in a studio, like the new BSkyB studio pictured, or for a night exterior powered by a portable generator, the harmonics generated by even small LED fixtures will accumulate and effect their power source adversely. To see which LED lights are power factor corrected or not, use this link  to see some of the results of my tests.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston


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